Most backpacks come with extra features, like hidden pockets and even earphone outlets. But most people aren’t aware of the purpose of that diamond patch on the front of many backpacks.

International magazineMarie Claire explained that those slits actually have very utilitarian roots.

Called “lash tabs,” these diamond-shaped patches, usually made of leather for durability and strength, allow the owner to insert a thin rope for carrying tools and other items.

“Originally, it was designed to carry an ice ax,” says Jamie Cormack, co-founder of Herschel in an interview.

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The feature was originally developed for hikers and mountain climbers.

“What a hiker or climber would attach depends on what type of adventure they are on—could be a water bottle, could be climbing rope, could be almost anything. But no matter what it is they are attaching, it would be something the person needs quick access to and thus the lashing square, so it’s on the outside of the pack,” adds JanSport’s Vice President of Marketing Ann Daw.

Marie Claire suggests using them if you have overweight baggage when traveling. By threading the laces of your sneakers (or any bulky items inside your bag) through the slits, you can free up some space in your bag.